1) Field of the Invention
The invention relates to a magazine for holding disk-type objects, in particular semiconductor wafers, during wet-chemical surface treatment in liquid baths, comprising a housing provided with openings for inlet and outlet of the bath liquid and means for introducing it into a liquid bath, and an insert which can be introduced into the housing for holding the workpieces to be treated directly, closely and flatly opposite one another.
2) Background Art
It is known that disk-type substrates, in particular single-crystal and polycrystalline semiconductor substrates composed, for example, of silicon, germanium and compound semiconductors such as gallium arsenide and indium phosphide or oxidic materials such as quartz, rubin, spinel or garnet, such as are generally produced by sawing up rod-type workpieces, are subjected, during the production process and, in particular, before further processing, to produce electronic devices, to many different kinds of cleaning and etching treatments which may serve, for example, to remove destroyed crystal regions from surface, or even to chemically alter the surface, in particular for instance by oxidation, oxide layer removal or hydrophilization.
It is important in such treatment steps that the cleaning solutions and etching solutions are distributed during the reaction uniformly and homogeneously over the entire surface of the wafers. At the same time, the cleaning and etching operations should also proceed at essentially the same rate over the entire wafer surface, so that, for example, nonuniform etching depths are avoided. Only in this way is it possible to obtain, for example, clean surfaces with as little flatness variation as possible and high surface parallelism, as are required by the manufacturers of electronic devices for the semiconductor wafers used.
In order to achieve such a uniform treatment of the surfaces with the cleaning solutions and etching solutions, a wide variety of devices have already been disclosed in the prior art such as, for instance, in DE-A-3-306 331 and DD-A-220 859. Thus, one of the design variations described therein is that the substrate to be etched is held at one surface with a suction head while a thorough mixing of the solution is achieved opposite the other surface which is to be etched, by rotating wafers which are provided with flow channels. In this case, however, only the processing of one wafer surface is possible.
In order however, to be able to process both surfaces, DD-A-220 859 provides an arrangement in which the wafers are held in an etching basket similar to a cage approximately parallel to one another and in a freely mobile fashion, so that a movement of the wafers to be etched relative to the etching basket is possible. In this case, the rotation of the etching basket results in a thorough mixing of the solution and simultaneously in a movement of the wafer relative to the etching basket, as a result of which the points of support of the wafer on the rods of the etching basket are continuously altered. However, in order to increase the thorough mixing of the treatment liquid, this embodiment requires the addition of smooth but not circularly shaped spacing disks which are also freely mobile and which also move relative to the etching basket and to the wafers to be processed. Under these conditions, however, the danger of mechanical damage to the wafers, of contamination by the material of the spacing disks or of the etching basket, or of a nonuniform application of the etching liquid if the spacing disks rest directly on the wafer surface of the wafer to be processed, is appreciably increased at the same time.
If, as is disclosed by DE-A-3 306 331, the treatment liquid is thoroughly mixed only by the wafers themselves or by the holding rods at the edge of the wafers, a more intense thorough mixing and greater removal rate, which results in lens-shaped cross section of the wafers, are produced in this edge region. Ring-shaped thickened sections which are produced by more intense removal at the wafer edge or in the interior of the wafer are also often observed.
Ultimately, therefore, the conventional etching processes are associated with a deterioration in the wafer geometry during the production of semiconductor wafers, in particular, as a result of the unfavorable wafer holding device. This disadvantage intensifies with increasing diameter of the substrates and makes itself felt, in particular, at diameters of &gt;100 mm, such as are increasingly required in device production.
The object of the invention is therefore to provide a holding device for treating wafers in liquid baths, with which a double-sided, uniform treatment with the bath liquid is possible without inhomogeneous reaction patterns occurring. In particular, the deterioration in quality during etching processes should be kept as low as possible so that the production of wafers with extremely flat and plane-parallel surfaces is possible.